The unsalicided poly resistor structures provided by conventional semiconductor integrated circuit technology, such as CMOS technology, typically provide an actual resistance value that can vary +/−30% or more from the nominal resistance value of the poly resistor structure. This type of variation is not acceptable for many applications that require precision resistors, for example, the termination resistors used in LVDS and PECL applications.
In some conventional techniques, the resistance variation is compensated for by providing additional poly resistors which can be switched into or out of either series or parallel combination with a target resistor, in order to compensate for the aforementioned variation of the target resistor. In such approaches, the resistance compensation is provided in discrete amounts, and the precision of the resistance compensation can be increased by increasing the number of compensation resistors that are available for selective switching into combination with the target resistor. It is desirable in view of the foregoing to provide a capability of increasing the precision with which a target poly resistor is compensated, without requiring a corresponding increase in compensating poly resistors.
Exemplary embodiments of the invention provide for the compensation of a target poly resistor by providing an active circuit that produces a negative resistance in parallel with the target poly resistor. This permits precise compensation for variations in the resistance value of the target poly resistor, without requiring any additional poly resistors as compensating resistances.